How about this?: Maybe the least surprising thing in “The Crash” is the discovery that teenage Don Draper lost his virginity to a prostitute.

Virtually everything else in “The Crash,” which in my book easily qualifies as the most unsettling installment of “Mad Men” to date, is unexpected, disorienting, terrifying or some combination thereof. The title, of course, refers to the events that bookend the episode: First, there’s the so-called “joy ride” Ken is forced to take with a pack of sadistic Chevy executives. I initially assumed it was a dream sequence, but then Ken shows up at the office, cuts all over his face and walking with a cane.

It’s a sign of the brilliant insanity of “The Crash” that Ken’s never-entirely-explained car crash is all but forgotten by the time Don, 72 sleepless, cranked-up hours later, lands with a thud on his shag-carpeted floor. It’s a literal crash that follows a more abstract one, as our protagonist, spurned by his mistress, creatively exhausted and battling a nasty cough, becomes unglued.

The narcotic paranoia and nonlinear storytelling of “The Crash” immediately call to mind last season’s standout, “Far Away Places.” But whereas Roger’s acid trip allowed him to peacefully accept the demise of his marriage and made him hungry for greater enlightenment, there is nothing reassuring or uplifting about Don’s forgotten weekend. It leaves him with just one realization: that he never wants to do that again.

But let’s start at the beginning and piece together this puzzle of an episode. Ken returns from his near-death experience with some bad news: Chevy wants the agency (which still doesn’t have a new name) to generate new campaign ideas every month through the end of the decade mostly, it seems, because they know they can make such extraordinary demands.

With another creative deadline looming, and at the suggestion of the utterly creepy Jim Cutler, Don and a handful of other employees get “energy serum” injected into their rear-ends. While it’s never spelled out explicitly, the shot is obviously some kind of amphetamine cocktail, and it turns everyone who takes it into manic, jittery messes.

Ken does a curious tap-dancing routine that renders Dawn speechless. At first it sounds like total nonsense, but on repeat viewings, it actually appears to be a protest about the degrading nature of being an account executive, as well as something of an explanation of that mysterious opening sequence. (“I’m their favorite toy … it’s my job to take them to dinner at 80 miles an hour… It’s my job to go hunting so they can fire off their guns an inch from my head, then laugh when I get startled, because it’s my job.”)

Meanwhile Stan, in between coming up with several hundred terrible ideas for Chevy, gets wounded in an impromptu game of William Tell, puts the moves on Peggy and confides in her about his cousin’s death in Vietnam. She advises him not to “dampen” the grief with drugs and sex, which is precisely what he does by hooking up with Wendy -- who, we later discover, is Frank Gleason’s daughter and is almost certainly doing the same.

As for Don, the drugs induce a flurry of flashbacks in which we learn the origins of the Madonna-whore complex we saw enacted so vividly last week. As a teenager living in a brothel with his stepmother, Dick/Don is nursed back to health, then deflowered by a kindly prostitute (on TV, is there any other kind?) who calls herself Aimée (rhymes with “may”). His stepmother finds out and beats Dick with a wooden spoon she had been using to stir oatmeal.

As an explanation of Don’s completely screwed-up relationship with women, this is about as on-the-nose as you can get. So too is the explanation he gives Ted back at the office Monday morning for not giving in to Chevy’s excessive demands: “Every time we get a car, this place turns into a whorehouse.”

And yet it works within the confines of this episode, which is otherwise so oblique and surreal that it calls to mind nothing so much as “Twin Peaks” (at least that was the consensus in my Twitter feed Sunday night). Collectively, “The Crash” gives us our closest glimpse yet of the inner workings of Don’s scrambled psyche, a place where client pitches and romantic overtures are virtually indistinguishable. When he calls Ginsberg and Peggy into his office and shares his idea, it becomes clear -- at least to us -- that the campaign he’s actually been working on all weekend is the one to win Sylvia back. (“What have you been doing the last three days?” wonders Peggy, once again speaking for all of us.)

While Don is going through his dark weekend of the soul, his poor daughter Sally goes through the latest in a long line of traumatizing incidents. Left alone to babysit while Megan has dinner with theater producers, she is quietly reading “Rosemary’s Baby” (never a good idea to do on your own) when she discovers a strange black woman has wandered in to the apartment. “I’m your grandma,” she claims. Sally is nobody’s fool, but she buys the woman’s story -- perhaps because there’s a part of her that wants it to be true, that longs to be taken care of, and for a connection to her distant father’s past.

Not to mention, the whole episode has unfolded in such a way that “Grandma Ida’s” explanation almost seems plausible and our minds race to fill in the blanks. Perhaps Don, in the midst of his speed-induced stupor, was contacted by the nanny of the real Don Draper? Or maybe he handed over his keys to a stranger during one of his blackouts? In the end, the truth turns out to be much simpler: “Grandma Ida” is, in fact, a burglar who took advantage of the door that Don left unlocked when he slipped off to lurk outside Sylvia’s kitchen.

It’s a testament to the writing and directing of this episode that it takes us nearly as long as Sally to figure out -- or accept, really -- who “Grandma Ida” actually is. As Sally tells her father, “I asked her everything I know, and she had an answer for everything. And then I realized I don’t know anything about you.”

One of the things that’s always been so enjoyable about “Mad Men” is its ability to inhabit several genres at once, to be a moody period piece, a witty caper and a broad farce, sometimes within the space a single episode. Over the last season or so, as “Mad Men” has advanced into the social and political maelstrom of the late '60s, it has added another genre to the list: horror.

When it comes to fictional portrayals of the decade, there’s an almost-unavoidable danger of being too didactic -- something that, alas, “Mad Men” has been guilty of this season. Lately, if you ask me, the show has been more successful when it goes for psychological horror over historical hand-wringing. “The Crash” seems like the culmination of a trend, beginning last season with “Mystery Date,” in which the pervasive anxiety of the era and Don’s inner torment combine in a way that’s profoundly unnerving for everyone involved. I suspect this episode will be a divisive one, but there’s little chance it left anyone sleeping peacefully, and that alone is enough to recommend it.

Pass the Seconal.

Stray thoughts:

--Betty, the aspiring political wife, is back to blond and several pounds lighter than when we last saw her.